JP3913252B2 - Optical time division multiplexing transmitter - Google Patents

Description

  The present invention relates to a transmission apparatus using an optical time division multiplexing (OTDM) system and a CS (Carrier Suressed) -RZ (Retern to Zero) modulation system. More specifically, the present invention relates to a technique for detecting and adjusting a carrier phase shift in an optical time division multiplexing apparatus using an optical time division multiplexing system and a CS-RZ modulation system.

  Conventionally, an optical time division multiplexing method is known as a signal multiplexing technique suitable for a high-speed and large-capacity optical transmission system. As a modulation technique suitable for such an optical transmission system, a CS-RZ modulation method is known.

  The optical time division multiplexing method is a method of multiplexing optical signal sequences of a plurality of channels by switching transmission channels at regular intervals. For example, it is possible to multiplex two-channel optical signal trains by switching the transmission channel for each bit period.

  The CS-RZ modulation method is a modulation method in which CS technology is added to the RZ method. Here, the RZ method is a method of providing a region where the signal value is zero between each signal bit. On the other hand, a method that does not provide a zero region is called an NRZ (Non Retern to Zero) method. The RZ method has an advantage that the timing control is easier than the NRZ method. On the other hand, the CS technique is a technique for shifting the phase of a carrier wave by a half wavelength between adjacent signal bits. When an overlap occurs between adjacent signal bits A and B, the light intensity of the composite signal component C in the overlap portion increases most when the phases of the carrier waves forming these signal bits coincide with each other. Cancel each other when they are shifted by half a wavelength. Therefore, by shifting the carrier phase of adjacent signal bits by a half wavelength, the light intensity of the portion where the adjacent signal bits overlap can be reduced, so that these signal bits can be completely separated (that is, the RZ method). It is easy to obtain a signal waveform of In a high-speed and large-capacity optical transmission system, it is desirable to shorten the interval between signal bits. Therefore, when the RZ system is adopted in such a high-speed and large-capacity optical transmission system, it is effective to use CS technology.

  In order to combine the above-described optical time division multiplexing system and CS-RZ system, the signal train of each channel may be formed from a carrier wave whose phase is shifted by half a wavelength. For example, if a two-channel signal sequence is formed from a carrier wave whose phase is shifted by a half wavelength and these signal sequences are time-division multiplexed, the carrier phase of adjacent signal bits is always shifted by a half wavelength. For example, in the case of time-division multiplexing a 4-channel signal sequence, the carrier phases of the first and third channels are matched, the carrier phases of the second and fourth channels are matched, and the first, The carrier phase of the three channels and the carrier phase of the second and fourth channels may be shifted by a half wavelength.

  As is well known, a bit signal is generated by modulating a carrier wave with a Mach-Zehnder type modulator or the like. Therefore, by controlling the timing for modulating the carrier wave, the phase of the carrier wave constituting the bit signal can be controlled. However, since the carrier wave has a very high frequency, it is not easy to control the phase of the carrier wave with high accuracy. In addition, the phase of the carrier wave may vary depending on temperature and the like. For this reason, in order to control the carrier phase difference between adjacent signal bits with high accuracy, a technique for measuring the phase difference with high accuracy is desired.

  The inventor of the present application has already proposed a technique for measuring the phase difference of a carrier wave according to Patent Document 1 below. In the technique of Patent Document 1, the phase difference is measured by measuring the light intensity by overlapping adjacent signal bits in the planar optical waveguide unit 310 (paragraph 0020 of FIG. 1, FIG. 1 and the like). reference). As can be seen from the above description, when adjacent signal bits are overlapped, the light intensity of the combined signal increases most when the phases of the carrier waves forming these signal bits match, and the phase is half-wavelength. When they are off, cancel each other. Therefore, by measuring the light intensity of the superimposed signal, the phase difference between the carrier waves constituting these signal bits can be detected.

  In the technique of Patent Document 1, combinations when overlapping adjacent signal bits of signal light output from the transmitter 100 (see FIG. 1 of Patent Document 1) are 1 · 1, 0 · 1, 1 · 0,0. -There are four types of 0. Here, when the light intensity when the bit signal is “1” is “1” (the light intensity when the bit signal is “0” is “0”), the superimposed signal bits are “1 · 1”. In this case, the optical intensity is “4” if the carrier phases of both signal bits match, but it is “0” if the carrier phases of both signal bits are shifted by a half wavelength. When the superimposed signal bits are “1 · 0” and “0 · 1”, the light intensity is “1” regardless of the phase difference of the carrier wave. Further, when the superimposed signal bits are “0 · 0”, the light intensity is “0” regardless of the phase difference of the carrier wave. Therefore, when the mark ratio of signal light (the existence ratio between “0” and “1”) is ½, the average light intensity detected by the planar optical waveguide portion (PLC portion in FIG. 2 of Patent Document 1) 310 is If the carrier phase of the signal bits coincides, (4 + 1 + 1 + 0) / 4 = 3/2, whereas if the carrier phase of the signal bits is shifted by a half wavelength, (0 + 1 + 1 + 0) / 4 = 1/2 It becomes. As described above, in the technique of Patent Document 1, the amount of change in light intensity (duty ratio) is three times (that is, 4.8 dB) between the case where the carrier phases of the signal bits match and the case where the signal bits are shifted by a half wavelength. It becomes.

This amount of change in light intensity cannot be said to be sufficiently large. Therefore, it has been difficult to accurately detect the phase difference of the carrier wave.
JP 2004-23537 A

  An object of the present invention is to provide an optical time division multiplex transmission apparatus capable of accurately detecting a carrier phase difference between adjacent signal bits.

  An optical time division multiplexing transmitter according to the present invention is an optical time division multiplexer that generates a time division multiplexed optical signal by time division multiplexing optical signal sequences of a plurality of channels generated so that the phases of carrier waves are shifted from each other. And extending the pulse width of the time division multiplexed optical signal to a width equal to or greater than the bit interval and superimposing the extended light of the adjacent bit on the extended light, and the superimposed light output from the optical interferor A light intensity detector for detecting the intensity.

  In the optical time division multiplex transmission apparatus according to the present invention, the optical interferometer is adapted to superimpose the extended light of adjacent bits on the extended light after extending the pulse width of the time division multiplexed optical signal to a width equal to or greater than the bit interval. Thus, it is possible to detect the light intensity using the interference at the intermediate portion between adjacent bits. For this reason, according to the present invention, the amount of change in light intensity can be made sufficiently large, and therefore the phase difference of the carrier wave can be detected with high accuracy.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the size, shape, and arrangement relationship of each component are shown only schematically to the extent that the present invention can be understood, and the numerical conditions described below are merely examples. .

First Embodiment First, an optical time division multiplex transmission apparatus according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram schematically showing the overall configuration of an optical time division multiplexing transmission apparatus according to this embodiment.

  As shown in FIG. 1, the optical time division multiplexing transmitter 100 according to this embodiment includes an optical time division multiplexer 110, an optical demultiplexer 120, a circulator 130, an optical interferometer 140, and an optical intensity detection. 150 and a temperature controller 160 are provided.

  The optical time division multiplexer 110 generates a time division multiplexed optical signal by time division multiplexing two-channel optical signal sequences generated so that the phases of carrier waves are shifted from each other. The optical time division multiplexer 110 includes an optical demultiplexer 111, optical modulators 112 and 113, and an optical coupler 114. The optical demultiplexer 111 branches the optical short pulse train P0 input from the outside into the optical short pulse trains P1 and P2. The optical modulator 112 modulates the optical short pulse train P1 according to the electrical pulse signal train E1 input via the electrical buffer 115, thereby generating the optical signal train S1. Similarly, the optical modulator 113 generates the optical signal sequence S2 by modulating the optical short pulse sequence P2 in accordance with the electrical pulse signal sequence E2 input via the electrical buffer 116. The optical modulators 112 and 113 have a function of controlling the temperature of an internal optical waveguide (not shown) in accordance with a control signal from the temperature regulator 160. By controlling the temperature of the optical waveguide, the refractive index of the optical waveguide can be controlled, and thereby the carrier phase of the optical signal trains S1 and S2 can be controlled. The optical coupler 114 combines the two-channel optical signal trains S1 and S2 to generate a time division multiplexed optical signal M0.

  The optical demultiplexer 120 extracts a part M1 of the time division multiplexed optical signal M0 output from the optical time division multiplexer 110.

  The circulator 130 sends the time division multiplexed optical signal M1 extracted by the optical demultiplexer 120 to the optical interferometer 140, and sends the superimposed light M2 output from the optical interferometer 140 to the optical intensity detector 150.

  The optical interferometer 140 extends the pulse width of the time division multiplexed optical signal M1 to a width equal to or greater than the bit interval, and superimposes the extended light of adjacent bits on the extended light. The superposed extended light is sent to the circulator 130 as superposed light M2. The optical interferometer 140 of this embodiment includes a half mirror 141 and first and second repetitive reflection interferometers 142 and 143. The half mirror 141 branches the time division multiplexed optical signal M1 into two branches. The first repetitive reflection interferometer 142 generates the extended light R1 from one of the branched time-division multiplexed optical signals and sends it back to the half mirror 141. The second repetitive reflection interferometer 143 generates the extended light R2 from the other of the branched time-division multiplexed optical signals and sends it back to the half mirror 141. The reciprocal optical path length between the half mirror 141 and the first repetitive reflection interferometer 142 is longer than the reciprocal optical path length between the half mirror 141 and the second repetitive reflection interferometer 143 by the 1-bit interval of the time-division multiplexed optical signal M1. It is arranged to be shorter. The detailed structure and principle of the optical interferometer 140 will be described later with reference to FIGS.

  The light intensity detector 150 detects the intensity of the superimposed light M2 output from the optical interferometer 140.

  The temperature controller 160 corresponds to the “regulator” of the present invention, and according to the detection result of the light intensity detector 150, the phase difference of the carrier waves constituting the optical signal trains S1 and S2 is a half wavelength. The temperature of the modulators 112 and 113 is controlled.

  Next, the optical interferometer 140 will be described in detail with reference to FIGS.

  FIG. 2 is a conceptual diagram showing the structure of the first repetitive reflection interferometer 142. The structure of the second repeated reflection interferometer 143 may be exactly the same as the structure of the first repeated reflection interferometer 142. As shown in FIG. 2, the repetitive reflection interferometer 142 includes a plurality of layers (four layers in the example of FIG. 2) of reflecting surfaces 201, 202, perpendicular to the optical axis direction of the time division multiplexed optical signal M 1. 203, 204. The reflectances of the reflecting surfaces 201 to 204 are, for example, 0.375, 0.2, 0.25, and 1. Since an antireflection film is formed on the back side of the reflection surface 204, multiple reflection can be ignored. When the time division multiplexed optical signal M1 is, for example, 80 Gbit / second, the temporal distance between the reflecting surfaces 201 and 202 is, for example, 2.25 picoseconds, and the temporal distance between the reflecting surfaces 202, 203 is, for example, 2.75 picoseconds. The temporal distance between the reflecting surfaces 203 and 204 is set to 5 picoseconds, for example. These temporal distances are 0.675 mm, 0.825 mm, and 1.5 mm, respectively, when converted to actual distances in vacuum.

  FIG. 3 is a conceptual diagram showing the intensity distribution of the signal light reflected by the reflecting surfaces 201-204. In FIG. 3, the vertical axis represents light intensity and the horizontal axis represents time. As can be seen from FIG. 3, a part of the signal pulse of the time-division multiplexed optical signal M1 is reflected by the reflecting surfaces 201 to 204, and the rest is transmitted. In FIG. 3, the reflected light on the reflection surfaces 201, 202, 203, 204 is indicated by reference numerals R 201, R 202, R 203, R 204. Then, the reflected lights R201 to R204 on the reflecting surfaces 201 to 204 are combined and output from the first repetitive reflection interferometer 142. The light intensity of each reflected light R201 to R204 is determined by the reflectance of the corresponding reflecting surface 201 to 204. The relative time positions of the reflected lights R201 to R204 are determined by the temporal distances of the reflecting surfaces 201 to 204. Therefore, by appropriately setting the reflectivity and the temporal distance of each of the reflecting surfaces 201 to 204, it is possible to obtain the combined reflected light (expanded light) R1 having a pulse width equal to or greater than the bit interval. The extended light R1 is sent to the half mirror 141.

  As described above, the structure of the second repeated reflection interferometer 143 is exactly the same as the structure of the first repeated reflection interferometer 142. Therefore, the second repeated reflection interferometer 143 outputs the extended light R2 having the same waveform as the extended light R1 (see FIG. 3) to the half mirror 141.

  Here, as described above, the reciprocal optical path length between the half mirror 141 and the first repetitive reflection interferometer 142 is more time-division multiplexed than the reciprocal optical path length between the half mirror 141 and the second repetitive interferometer 143. The optical signal M1 is shorter by the interval of 1 bit. Accordingly, the extended light R1 corresponding to each bit signal (that is, the extended light generated by the first repetitive reflection interferometer 142) is extended light R2 corresponding to the next bit signal (that is, the second repetition light). Simultaneously with the extended light generated by the reflection interferometer 143, the light reaches the half mirror 141. For this reason, the half mirror 141 always superimposes and outputs two consecutive bit signals. Further, as described above, the time division multiplexed optical signal M1 is composed of two-channel optical signal sequences S1 and S2 whose carrier phases are shifted from each other. Therefore, the superimposed light M2 output from the half mirror 141 is a composite wave of bit signals whose carrier wave phases do not match. In such a case, the light intensity of the superimposed light M2 changes according to the magnitude of the phase difference of the carrier wave.

  FIG. 4 is a schematic waveform diagram for explaining the operation of the optical interferometer 140.

  4A shows the case where the optical signal sequences S1 and S2 have the same carrier phase (that is, the carrier phase difference is zero). In FIG. 4A, (a1) is the signal logic of the time division multiplexed optical signal M1 input to the interferometer, and (a2) is the waveform of the time division multiplexed optical signal M1. As described above, the first and second repetitive reflection interferometers 142 and 143 extend the pulse width of the time division multiplexed optical signal M1 (see (a6) in FIG. 4A). For this reason, when the logical value “1” continues, overlap between adjacent bits occurs, and the optical signal intensity increases. Therefore, the extended lights R1 and R2 generated by the first and second repetitive reflection interferometers 142 and 143 have waveforms as shown in (a3) and (a4) of FIG. These extended lights R1 and R2 are superimposed by the half mirror 141. Thus, the superimposed light M2 output from the optical interferometer 140 has a waveform as shown in (a5) of FIG. FIG. 5A shows a part of the result of simulating an actual waveform of the schematic superimposed wave shown in (a5) of FIG. As shown in FIG. 5A, when the carrier wave phases of the optical signal sequences S1 and S2 are the same, the light intensity of the portion where 1 continues is very high.

  On the other hand, FIG. 4B shows a case where the carrier wave phases of the optical signal sequences S1 and S2 (see FIG. 1) are shifted by a half wavelength. As shown in (b1) of FIG. 4 (B), the signal logic of the time division multiplexed optical signal M1 is the same as in FIG. 4 (A). Therefore, as shown in (b2) of FIG. 4B, the waveform of the signal M1 is the same as that in FIG. 4A. Also in this case, the first and second repetitive reflection interferometers 142 and 143 extend the pulse width of the time division multiplexed optical signal M1. However, in the case of FIG. 4B, the carrier phases of adjacent bits are shifted from each other by a half wavelength, so even if the overlap between adjacent bits occurs in the portion where the logical value '1' continues, it cancels out. For this reason, since the light intensity in the overlapping portion becomes zero, the extended lights R1 and R2 generated by the first and second repetitive reflection interferometers 142 and 143 are (b3) in FIG. The waveform is as shown in (b4). Further, in the case of FIG. 4B, when these extended lights R1 and R2 are added by the half mirror 141, the bits of the logical value “1” cancel each other. Thus, the superimposed light M2 output from the optical interferometer 140 has a waveform as shown in (b5) of FIG. FIG. 5B is a part of the result of simulating an actual waveform of the schematic superimposed wave shown in FIG. 4B (b5). As shown in FIG. 5B, when the carrier wave phases of the optical signal trains S1 and S2 are the same, the light intensity of the portion where 1 continues is zero.

  5A and 5B, when the carrier phase is the same between adjacent bits, the average intensity of the superimposed light M2 is higher than when the carrier phase is shifted by a half wavelength. I understand that. Hereinafter, a specific method for calculating the average intensity will be described.

As described above, in the present embodiment, the pulse width of the optical signal bit reflected by the first repetitive reflection interferometer 142 (see FIG. 1) is expanded, thereby overlapping the previous bit and the next bit. Furthermore, the extended light R2 of the previous bit is superimposed on the extended light R1 generated in this way by the half mirror 141. This extended light R2 also overlaps the bit before the previous bit (that is, the bit before the extended light R1) and the next bit of the previous bit (that is, the extended light R1). Therefore, the superimposed light M2 output from the half mirror 141 is affected by the previous bit, the previous bit, and the next bit of the extended light R1. For this reason, the light intensity of the extended light R1 changes depending on not only the signal logic of the extended light R1 but also the signal logic of the previous bit, the previous bit, and the next bit. For this reason, the light intensity of the extended light R1 can take 2 ⁴ (= 16) values. In addition, these 16 kinds of extended light intensity change according to the phase shift of the carrier wave forming the optical signal sequences S1 and S2 (see FIG. 1).

  Here, in order to obtain the light intensity of the extended light R1, the area of the optical waveform of the extended light R1 may be calculated. For example, from the waveform in FIG. 5A, the extended optical intensity can be obtained when the carrier phase of adjacent signal bits is the same, and from the waveform in FIG. The extended light intensity when the phase is shifted by a half wavelength can be obtained. Furthermore, the extended light intensity corresponding to FIGS. 5A and 5B can be estimated using (a5) in FIG. 4A and (b5) in FIG. 5B.

  FIG. 6 is a table showing results of estimating the light intensity of the extended light R1 using (a5) of FIG. 4 (A) and (b5) of FIG. 4 (B). In FIG. 6, x is the pulse width of the diffused light R1, and y is the 1-bit length of the extended light R1 (for example, 12.5 picoseconds in the case of 80 Gbit / s signal light) (FIG. 4 ( (Refer to (a6) of A)).

  It can be considered that the average intensity of the extended light R1 is an average value of the 16 kinds of extended light intensity described above. Therefore, in the example of FIG. 6, the average value I1 of the extended light intensity when the carrier wave phases of adjacent signal bits are the same is given by the following equation (1), and the carrier wave phase is shifted by a half wavelength: The average value I2 is given by the following equation (2). Then, the following expression (3) is given from the expressions (1) and (2). Here, d is the duty ratio of the optical signal bits before and after expansion, and therefore d = x / y. As understood from the equation (3), the intensity ratio I1 / I2 depends on the duty ratio d.

I1 = 64x + 24y (1)
I2 = 16x + 8y (2)
I1 / I2 = (64d + 24) / (16d + 8) (3)

  FIG. 7A is a graph showing the relationship between the intensity ratio I1 / I2 and the duty ratio d, where the vertical axis is the intensity ratio I1 / I2 and the horizontal axis is the duty ratio d. As can be seen from FIG. 7A, when the duty ratio d is larger than “1”, the intensity ratio I1 / I2 increases depending on the duty ratio d. Thus, it can be seen that the intensity ratio I1 / I2 increases when the pulse width of the optical signal bit is expanded using the optical interferometer 140 (that is, when the duty ratio d is made larger than ‘1’). As can be seen from FIG. 7A, for example, when the duty ratio d is 1.3, the intensity ratio I1 / I2 is about 3.4 (that is, 5.3 dB), and a sufficiently large intensity ratio I1 / I2 is obtained. .

  FIG. 7B is a graph showing an example of the relationship between the carrier phase difference between adjacent signal bits and the optical signal intensity, where the vertical axis represents the optical signal intensity [dBm] and the horizontal axis represents the phase difference [adim]. As shown in FIG. 7B, in the optical time division multiplex transmission apparatus 100 according to this embodiment, the extended optical intensity when the carrier phase of adjacent signal bits is the same and the carrier phase are shifted by a half wavelength. In this case, the ratio of the light intensity to the extended light intensity is sufficiently large (5.3 dB in the example of FIG. 7B), so that the change of the light intensity with respect to the change of the carrier phase becomes large. It becomes easy to improve.

  As described above, according to the optical time division multiplex transmission apparatus 100 according to this embodiment, since the optical interferometer 140 is provided, it is possible to accurately detect the carrier phase difference between adjacent signal bits.

Second Embodiment Next, an optical time division multiplex transmission apparatus according to a second embodiment of the present invention will be described with reference to FIG.

  In this embodiment, an interferometer is configured using a fiber Bragg grating (FBG). Since the configuration of other parts is the same as that of the first embodiment, description thereof is omitted.

  FIG. 8 is a conceptual diagram schematically showing the configuration of the interferometer 800 according to this embodiment.

  As shown in FIG. 8, the interferometer 800 includes a fiber Bragg grating 810 and a covering member 820 covering the fiber Bragg grating 810. The fiber Bragg grating 810 is formed with a first grating region 811 and a second grating region 812 with the phase shift region 813 interposed therebetween.

  The first and second grating regions 811 and 812 have a plurality of reflecting surfaces (see FIG. 2), similarly to the repetitive reflection interferometers 142 and 143 (see FIG. 1) according to the first embodiment. Each reflecting surface reflects a part of the time-division multiplexed optical signal M1 and transmits the rest.

  The phase shift region 813 transmits the time division multiplexed optical signal M1 as it is. The phase shift region 813 is provided to set a difference in the reciprocal optical path length between the light input / output end 801 and the first and second grating regions 811 and 812. That is, the reciprocal optical path length between the optical input / output end 801 and the first grating region 811 is 1 than the reciprocal optical path length between the optical input / output end 801 and the second grating region 812. The length of the phase shift area 813 is set so as to be shorter by the bit interval.

  Next, the operation principle of the interferometer 800 shown in FIG. 8 will be described.

  The time division multiplexed optical signal M1 is output from the circulator 130 (see FIG. 1), and input to the fiber Bragg grating 810 from the input / output terminal 801. The optical signal M1 reaches the first grating region 811. As described above, a part of the optical signal M1 is sequentially reflected by each reflecting surface of the grating 811. Then, these reflected lights are combined and output from the light input terminal 801. Thereby, the extended light R1 similar to that of the first embodiment is obtained (see FIG. 3).

  The optical signal component that has passed through the first grating 811 reaches the second grating region 812. Part of this optical signal component is sequentially reflected by each reflecting surface of the second grating 812. Then, these reflected lights are combined and output from the light input terminal 801. Thereby, the extended light R2 similar to the first embodiment is obtained.

  As described above, the round trip optical path length between the optical input / output end 801 and the first grating region 811 is larger than the round trip optical path length between the optical input / output end 801 and the second grating region 812. Shorter by 1 bit interval. Therefore, the extended light R1 corresponding to each bit signal reaches the optical input / output terminal 801 simultaneously with the extended light R2 corresponding to the previous bit signal. For this reason, the optical input / output terminal 801 always superimposes and outputs two consecutive bit signals.

  Since the other operation | movement which concerns on the optical time division multiplexing transmission apparatus which concerns on this embodiment is the same as that of 1st Embodiment, description is abbreviate | omitted.

  As described above, according to the optical time division multiplex transmission apparatus according to this embodiment, since the interferometer 800 is provided, the carrier phase difference between adjacent signal bits can be accurately detected as in the first embodiment. can do.

  In addition, since the interferometer 800 is configured with a fiber Bragg grating, there is an advantage that the configuration is simplified.

  In the embodiment described above, the optical time division multiplex transmission apparatus that multiplexes the two optical signal sequences S1 and S2 has been described as an example. However, the optical time when four or more optical signal sequences are multiplexed is described. The present invention can also be applied to a division multiplexing transmitter.

1 is a block diagram schematically showing an overall configuration of an optical time division multiplex transmission apparatus according to a first embodiment. FIG. It is a conceptual diagram which shows the structure of the interferometer which concerns on 1st Embodiment. It is a conceptual diagram for demonstrating operation | movement of the interferometer which concerns on 1st Embodiment. It is a typical waveform diagram for demonstrating operation | movement of the interferometer which concerns on 1st Embodiment. It is a wave form diagram for demonstrating operation | movement of the interferometer which concerns on 1st Embodiment. It is a chart for demonstrating operation | movement of the interferometer which concerns on 1st Embodiment. It is a graph for demonstrating operation | movement of the interferometer which concerns on 1st Embodiment. It is a conceptual diagram which shows the structure of the interferometer which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Optical time division multiplexing transmitter 110 Optical time division multiplexer 111,120 Optical demultiplexer 112,113 Optical modulator 114 Optical coupler 115,116 Electric buffer 130 Circulator 140 Optical interferometer 150 Optical intensity detector 160 Temperature controller

Claims (6)

An optical time division multiplexer that generates a time division multiplexed optical signal by time division multiplexing optical signal sequences of a plurality of channels generated so that the phases of carrier waves are shifted from each other;
Extending the pulse width of the time division multiplexed optical signal to a width equal to or greater than the bit interval, and superimposing the extended light of adjacent bits on the extended light; and
A light intensity detector for detecting the intensity of the superimposed light output from the optical interferometer;
An optical time division multiplex transmission apparatus comprising:   The optical time division multiplex transmission apparatus according to claim 1, further comprising an optical demultiplexer that extracts a part of the time division multiplexed optical signal output from the optical time division multiplexer.   A circulator for sending the time-division multiplexed optical signal extracted by the optical demultiplexer to the optical interferometer and sending the superposed light output from the optical interferometer to the optical intensity detector; The optical time division multiplex transmission apparatus according to claim 2.   And a controller for controlling the optical time division multiplexer so that a phase difference of the carrier wave constituting the adjacent optical signal sequence becomes a half wavelength according to a detection result of the light intensity detector. The optical time division multiplex transmission apparatus according to any one of claims 1 to 3. The optical interferometer includes a half mirror that bifurcates the time-division multiplexed optical signal, and a first repetitive reflection interferometer that generates the extended light from one branched time-division multiplexed optical signal and sends it back to the half mirror. And a second repetitive reflection interferometer that generates the extended light from the other branched time-division multiplexed optical signal and sends it back to the half mirror, and
The first and second repetitive reflection interferometers so that the reciprocal optical path length between the half mirror and the first and second repetitive reflection interferometers is shifted by one bit interval of the time division multiplexed optical signal. Was placed,
The optical time division multiplex transmission apparatus according to any one of claims 1 to 4, The optical interferometer generates the extended light from the first grating region that generates the extended light from the time division multiplexed optical signal, and the time division multiplexed optical signal that has passed through the first grating region. A fiber Bragg grating comprising a second grating region; and
The first and second optical path lengths between the optical input / output end of the fiber Bragg grating and the first and second grating regions are shifted by one bit interval of the time division multiplexed optical signal. 2 grating regions were formed,
The optical time division multiplex transmission apparatus according to any one of claims 1 to 4,

Images